At the beginning of this year, my friend drew an idea for a eurorack modular synth module on the back of a coaster and asked if I could make it. The idea was to take a trigger signal (a kind of digital signal which triggers a sound on another module) and to send it to one of eight outputs, based on 3 levels of random A/B decisions, where the probability of A/B can be set by a potentiometer. A bit like a Galton board, except that the distribution is uniform if the A/B probability is set to 50% at each decision. A module that does one such A/B decision already exists under the name of a Bernoulli Gate. However, we would need 7 such Bernoulli gates (1+2+4) to end up with 8 outputs. I first experimented a bit with 555 timers and flipflops to create one Bernoulli gate, but quickly realized I’d need way too many components to make it economical. So in the end I decided to go for the microprocessor approach. Having never before programmed a microprocessor, but remembering from my student years the Microchip brand, I ordered a few PIC16 controllers with enough analog inputs for the potentiometers and enough outputs. After struggling a bit in C because of implicit type conversions and the very limited memory available on the microprocessor, I finally managed to get it to work. I designed a prototype PCB and my friend designed a faceplate, which we also had printed on PCB. This is what that first prototype looks like:

Oddity PCB

We added two extra features: the possibility to loop the last 2-8 or 16 steps, and a toggle switch to change the first A/B switch into a split, enabling two groups of four outputs.

It was really cool to go from breadboard experiments with some basic components, to programming and simulating the idea in C and then see it work for real on the prototype. Although I have to say that the MPLAB software to program the microcontroller is quite buggy. I’m wondering if there are better alternatives out there.

This is a very short demonstration of the module:

The module is perfect for adding some randomness to your music, and is very intuitive to use. If you’re into modular synths and would like to know more about this module, don’t hesitate to reach out!